Using blinking optical tweezers to study cell rheology during initial cell-particle contact

Area of Science:

• Cellular mechanics and biophysics
• Immunology and innate immunity

Background:

• Phagocytosis is a key innate immunity process involving cell membrane engulfment of particles.
• Understanding phagocytosis mechanics is limited by techniques lacking simultaneous high-resolution binding dynamics and viscoelasticity measurements.

Purpose of the Study:

• To develop and apply a novel technique for localized characterization of cellular mechanical properties during early phagocytosis.
• To investigate the binding dynamics and viscoelastic response of macrophages during particle engulfment.

Main Methods:

• Utilized holographic optical tweezers to attach immunoglobulin-G-coated microparticles to macrophages.
• Employed a novel technique to simultaneously resolve contact regions below optical resolution and measure time-resolved rheological properties.
• Investigated the effect of cytochalasin D on cellular mechanics and actin cortex behavior.

Main Results:

• The technique successfully resolved contact dynamics and measured viscoelastic cellular response consistent with power law rheology.
• Contact radius increased on a timescale of ~30 s, converging within minutes.
• Cytochalasin D treatment increased cellular compliance and fluidization of the actin cortex without affecting binding dynamics.

Conclusions:

• The developed technique provides simultaneous access to binding dynamics and cellular viscoelasticity during phagocytosis.
• Findings reveal insights into the mechanical regulation of early phagocytosis and the role of the actin cortex.
• Established upper boundaries for actin depolymerization timescales during early phagocytosis.